1. Technical Field
This invention relates generally to rechargeable batteries, and more specifically to rechargeable batteries with safety circuits.
2. Background Art
Portable electronic devices, such as cellular telephones, pagers, and two-way radios for example, derive their portability from batteries having rechargeable cells. These batteries allow these devices to slip the surly bonds of power supplies tethered to the wall and to travel wirelessly with the user wherever he may go.
While some may think that a rechargeable battery is simply a rechargeable cell and a mechanical housing, nothing could be further from the truth. Rechargeable battery packs often include circuit boards, electronic circuitry, mechanical housings or structural assemblies, and electronic or mechanical protection components. Simply put, a rechargeable battery pack is a system of components working in harmony to safely deliver power to a portable electronic device.
One of the most fundamental circuits in a battery pack is the protection circuit. Rechargeable battery performance, especially with respect to those having cells constructed of lithium-based materials, may be severely compromised if the cell within the battery pack is over or under charged. For this reason, most all battery packs today include one form of safety circuit or another. Typical safety circuits include voltage and current limits. As such, when the voltage across the cell in a battery pack becomes too high or too low, the safety circuit will open switches within the pack, thereby temporarily “turning off” the battery pack. Similarly, if the current flowing either into or out of the cell gets too high, the safety circuit will momentarily turn off the battery pack.
Not too long ago, most rechargeable battery packs were detachable from the devices they powered. For instance, a mobile telephone user could remove the battery pack from the mobile telephone for charging or replacement. However, as today's modern electronic devices are becoming smaller and smaller, many devices are integrating the rechargeable battery into the device. As such, the user does not have access to the battery pack.
One problem associated with integrated batteries is that of host current drain during storage. Some electronic devices drain small amounts of current from the battery pack even when they are OFF. As such, an issue of concern is the amount of current drain that occurs between the electronic device with the integrated battery is manufactured and the time when it is first charged by a consumer. During this time, which could be months, the circuitry in the host device can be generally consuming energy. This energy consumption causes battery discharge. If the charge level decreases too much, a condition known as over-discharge, the performance of the battery can be compromised
There is a need for a battery assembly that can reduce an amount of current being drained from the battery during storage or similar conditions.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.